In the case of performing three dimensional shape measurement with respect to a reflective area such as a mirror, a metal, or a water surface; it is necessary to implement a measurement method that is suitable for reflective areas. For that reason, it is first necessary to identify a reflective area. As a method of identifying a reflective area, a method is known in which a specular area is identified by comparing the luminance distribution of normal reflection light in a captured image with the brightness value representing the degree of specularity in the imaging environment.